The goal of this project is to evaluate carbon nanotubes (CNTs) as lower impedance, smaller electrodes for neurostimulation, using deep brain stimulation (DBS) as a test case. Lower impedance of the electrode-tissue interface results in lower power consumption, as a smaller voltage is required to achieve the same charge injection. Low power consumption extends battery life and decreases the size of the batteries and thus of the implanted device. The size of stimulating electrodes is limited by the minimum charge injection required for effective stimulation and the impedance of the electrode-tissue interface. As well, the size of the electrode is an important factor in the insertion damage created by the electrode and the specificity of the volume that can be stimulated. Lower impendence and smaller electrodes will lead to less damaging electrodes and a combination of smaller and longer lasting batteries. We will compare the performance of CNT electrodes to AIROF and traditional platinum electrodes using quantitative in vitro measurements. We expect to increase the reversible charge injection capacity, Qinj, (in C/cm2) by 230% over the same-sized Pt electrode and exceed AIROF electrodes by 200% in the water electrolysis window, or to reduce the size of the electrode from a standard 0.06 cm2 to 0.026 cm2 while maintaining the same charge injection capacity, or a combination thereof. We expect to reduce the impedance, Z, by 65% vs a platinum electrode and 40% vs an AIROF electrode of the same size. The specific aims of this project are: (1) Quantify the effect of CNT morphology (length, density, orientation) on charge injection and interfacial impedance, and identify those combinations that increase charge injection and reduce interfacial impedance. The charge injection capacity will be determined by measuring voltage transients during in vitro current pulse stimulation, and the charge injection mechanisms will be determined by cyclic voltammetry. The interfacial impedance will be measured in vitro by electrochemical impedance spectroscopy. (2) Using the best electrode configuration from Aim #1, evaluate chemical modification of the CNT surface, such as oxygen functional groups, e.g., =O and -COOH, to further increase the charge injection capacity and decrease the impedance. (3) Test the top 5 electrode configurations from Aim #2 in vitro with rat neural tissue for a glial response and assess the CNT electrode performance (Qinj, Z, power consumption) in the presence of neural tissue and compare the performance to platinum and AIROF electrodes. Further, the electrodes will undergo chronic pulse testing in solution to evaluate the stability of charge injection capacity and interfacial impedance. The outcome of this project will be a comprehensive in vitro assessment of carbon nanotubes, grown with a platinum catalyst, as highly efficient neural stimulation electrodes. If realized, it will lead to neural stimulation electrodes that are smaller, limiting insertion damage, and consume less power, thereby reducing the size and increasing the lifetime of batteries.